The present invention relates to videoconferencing, and more particularly, to a technique for recording a videoconference during a conference session for future viewing.
In a typical videoconference system as illustrated in FIG. 1, a plurality of conference stations 1 communicate with each other through a conference bridge 10 over data network 2. During a videoconference session, each of the conference stations 1 participating in the conference generates a videoconference signal (e.g., from a video camera) and transmits it to the conference bridge 10 which routes the video signal to each of the other conference stations for presentation on terminal screens. For the purpose of viewing the video signal in real time, the original video signal generated from each videoconference station is encoded into a xe2x80x9cwire formatxe2x80x9d before it is transmitted to the conference bridge so that the video images can be streamed to the receiving stations.
Most videoconferences presently in use are implemented using digital techniques. The digital techniques usually involve encoding the information for transmission over a network to other conferees. A variety of encoding algorithms exist, and a trade-off among various parameters is often performed to select the encoding algorithm.
One parameter relevant to selection of the encoding algorithm is latency. Latency refers to a time delay between the transmission of the video image to the receipt of that video image by other conference members. During real time videoconferencing, longer latency is considered a negative. Specifically, high latency means that the images are significantly delayed from the time of transmission, until the time they are viewable by the viewer. This is similar to a satellite delay seen in long distance telephone calls. Moreover, if the latency of the image is different from that of the audio, then the sound will not be synchronized with the lip movement of the speaker, resulting in poor videoconferencing. This problem can occur if the latency for the video is so long that it delays the video by more than the audio.
Unfortunately, if a complex signal processing and image compression algorithm is used that requires long blocks of data to encode and relatively large number of calculations, then for a given fixed processing power, latency will increase. The reason for this limitation is that the more complex the algorithm is, the more time it typically takes to process the signals. If the image compression/encoding algorithm is too complicated, it will take a relatively long time to encode the image and then decode the image at the receiving end. Thus, minimization of latency can only be achieved through less complex image encoding algorithms.
On the other hand, in order to achieve extremely high image quality, it is desirable to use more advanced signal processing and image encoding/decoding algorithms. These advanced algorithms allow very high quality images to be reconstructed even from lower bit rates, which are needed for transmission over the media.
In view of the above, it can be appreciated that the requirements of latency and image quality are, in some sense, conflicting. More specifically, high image quality requires very complex encoding algorithms in order to insure accurate image reconstruction. However, such complex algorithms increase latency, and thus, result in a situation where high delay diminishes the user-friendliness of the system.
In view of the above, there exists a need in the art for an efficient technique to provide an image in a videoconference that is both high quality and low latency.
The present invention provides a technique of recording a videoconference in which the videoconference can be recorded independently of the real time transmission of the video signal. Thereafter the recorded video can be transmitted to others desiring to review it later. Different encoding mechanisms can be utilized for the real time transmission and the storage for later transmission.
In particular, a first encoder is provided for encoding the original video signal into a first format that is suitable for real time transmission to the conference bridge to be routed to other participating stations, and a second encoder is provided for encoding the original video signal into a second format as desired by the user.
The first and second encoders work independently of each other. The first encoder uses a low latency algorithm for real time transmission of the video signal. This encoder sacrifices some quality to achieve real time transmission with low latency within an allocated bandwidth. The second encoder is used for archival and storage of the image. This second encoder achieves higher quality, at the expense of latency. However, since the second encoder is for storage and later review of the image, latency is not in issue and may be sacrificed, since recording the image after a one or more seconds delay is acceptable.
In an enhanced embodiment, the stored image is associated with a list of conference members and associated network addresses. The higher quality image may then be later transmitted, in non-real time, to conference members, either automatically or at a conference member""s request. It is also possible to implement the two encoders using different parameters with, or variations of, the same algorithms.